BEIRUT -- Rebels backed by captured tanks launched a fresh offensive on a government complex housing a police academy near the northern city of Aleppo on Sunday, while the government hit back with airstrikes to try to protect the strategic installation, activists said.

If rebels capture the complex on the outskirts of Aleppo, it would mark another setback for President Bashar Assad. In recent weeks, his regime has lost control of key infrastructure in the northeast including a hydroelectric dam, a major oil field and two army bases along the road linking Aleppo with the airport to its east.

Rebels also have been hitting the heart of Damascus with occasional mortars shells or bombings, posing a stiff challenge to the regime in its seat of power.

On Saturday, opposition fighters in the eastern province of Deir el-Zour overran a military post believed to have once been the site of a partly built nuclear reactor that Israeli warplanes bombed in 2007.

A year after the strike, the U.N. nuclear watchdog determined that the destroyed building's size and structure fit specifications of a nuclear reactor. Syria never stated the purpose of the site known as Al-Kibar.

After the bombing, the regime carted away all the debris from the destroyed building and equipment from the two standing structures, analysts said, adding that the rebels were unlikely to have found any weapons in the abandoned complex.

There were troops in the area until this weekend. It was not clear what the site was being used for most recently.

"It's more or less a shell because the Syrians decided to remove everything inside the buildings," said Mustafa Alani, an analyst with the Gulf Research Center in Geneva. "I don't think there's anything left really of any value for the rebels."

Separately, rebels have been trying for months to storm the government complex west of Aleppo in the suburb of Khan al-Asal, according to Rami Abdul-Rahman, the director of the Britain-based Syrian Observatory for Human Rights.

The facility also includes several smaller army outposts charged with protecting the police academy inside the compound.

The SANA state news agency said regime troops repelled the rebel attack on the police academy, inflicting heavy losses and destroying four armoured vehicles and three cars fitted with machine-guns. There was no word on government casualties.

Aleppo has been the scene of some of the heaviest fighting of Syria's nearly 2-year-old conflict.

In July, rebels launched an offensive on the city, the country's largest and one-time commercial capital, and quickly seized several neighbourhoods. The battle has since devolved into a bloody stalemate, with heavy street fighting that has left whole districts in ruins and forced thousands to flee.

A key focus for the rebels as they try to capture the city is Aleppo's international airport, which they have been attacking for weeks.

Regime forces also fired an apparent ground-to-ground missile Sunday on the town of Tal Rifat, some 30 kilometres (20 miles) north of Aleppo, the Observatory said. There was no immediate word on casualties.

The report follows similar strikes last week on impoverished rebel-held Aleppo neighbourhoods that killed at least 60 people.

Also on Sunday, prominent Syrian comedian Yassin Bakoush was killed in Damascus after apparently being caught in the crossfire between rebels and government troops.

Bakoush, 75, was known for playing characters that were likeable but naive and dim-witted. SANA said he is survived by11 children.

SANA said Yassin Bakoush was killed by a rebel mortar round that landed on his car in the Yarmouk Palestinian refugee camp in southern Damascus, which has seen heavy fighting in recent months. However, the anti-regime Observatory said Bakoush was killed when a rocket-propelled grenade launched by government forces slammed into his car.

French freelance photographer Olivier Voisin, who was wounded on Thursday in Syria and taken to Turkey for treatment, died of his wounds at an Istanbul hospital, the French Foreign Ministry said Sunday.

Voisin is the second French journalist this year to be killed while reporting on the civil war, which has proven to be one of the most dangerous conflicts for reporters to cover.

In Lebanon, two people were killed by Syrian shells and gunfire that landed on Lebanese territory near the border.

The state-run National News Agency in Lebanon said a man was killed and his brother was wounded by shells that slammed into the town of al-Hisheh in the Wadi Khaled area of the north, while another man was killed by gunfire in the area of al-Buqaiaa.

The deaths added to tensions in the area which has seen an escalation of violence in recent days. The civil war in Syria has increasingly spilled over into Lebanon with almost daily reports of cross-border shelling or gunfire in border areas.

The United Nations says at least 70,000 people have been killed since the uprising against Assad's authoritarian rule began nearly two years ago.

Efforts to stop the bloodshed so far have failed, leaving the international community at a loss of how to end the civil war.

A senior opposition leader said Sunday that his umbrella group has suspended participation in meetings with its Western backers and their Arab allies because of their indifference over the regime's attacks on the Syrian people in Aleppo and other cities.

"Assad has reached the stage of real genocide amid Arab silence and we renounce that," George Sabra, vice-president of the Syrian National Coalition, said in Cairo after meeting Arab League chief Nabil Elaraby.

On Friday, the Coalition said its leaders would not travel to Washington or Moscow for any talks to protest the international community's "silence over crimes committed by the regime." It also said opposition leaders would boycott a meeting next month in Rome of the Friends of Syria, which includes the United States and its European allies.

In Washington, the State Department condemned rocket attacks on Aleppo, saying in a statement late Saturday the strikes are the "latest demonstrations of the Syrian regime's ruthlessness and its lack of compassion for the Syrian people it claims to represent."